MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY
Pollution analysis of a leaf of a holm oak (Quercus ilex). The leaf can be used to measure the amount of particulate matter present in the air where the tree is growing. The leaf is treated and folded into a box (right) for analysis. The box is placed in a Bartington dual-frequency magnetic susceptibility device. Comparison of the response of the sample to a high and low frequency magnetic field allows the amount of tiny superparamagnetic particles on the leaf to be calculated, which can be used to calculate the amount in the air. This sample was part of a study of airborne particulate matter levels in the city of Rome, Italy.
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